retrofit shower floor questions

I'm thinking about using a "retrofit shower floor" to replace my bathtub. I put the link to what I'm looking at below.

Does anyone know how these line up with the existing drain. Are the drain locations farily standard in a bathtub and this retrofit floor most likely will line up well, or are the drain locations a bit more variable and might I have to do some alteration with the drain, chipping out concrete and such?

Also I've read the drain size code is different with a shower vs. bathtub, anyone know how that changes with this method. Retrofit floor has correct drain size or........??

(home is on concrete slab foundation)

http://www.*********.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053